The word tsunami (pronounced tsoo-nah’-mee) is composed of the Japanese words “tsu” (which means harbor) and “nami” (which means “wave”). A tsunami is a series of large waves of extremely long wavelength and period usually generated by a violent, impulsive undersea disturbance or activity near the coast or in the ocean; caused by earthquakes or volcanic eruptions under the sea. When a sudden displacement of a large volume of water occurs, or if the sea floor is suddenly raised or dropped by an earthquake, big tsunami waves can be formed.  The waves travel out of the area of origin and can be extremely dangerous and damaging when they reach the shore.

        Often the term, “seismic or tidal sea wave” is used to describe the same phenomenon, however, the terms are misleading, because tsunami waves can be generated by other, non-seismic disturbances such as volcanic eruptions or underwater landslides, and have physical characteristics different from tidal waves. The tsunami waves are completely unrelated to the astronomical tides – which are caused by the extraterrestrial, gravitational influences of the moon, sun, and the planets. Thus, the Japanese word “tsunami”, meaning “harbour wave” is the correct, official, and all-inclusive term.

EARTHQUAKE

An earthquake happens when energy suddenly releases inside the Earth. This release causes strong shaking on the Earth’s surface. It usually occurs because the Earth’s crust moves.

The place where an earthquake starts is called the epicenter. People often feel the strongest shaking near this point.

The released energy travels through the Earth as seismic waves. Scientists measure these waves with instruments called seismographs.

Scientists also measure earthquake size by using the Richter scale or the Moment scale. Small earthquakes, below magnitude 3, are hard to feel. However, earthquakes above magnitude 7 can cause serious damage.

Another method is the Mercalli scale, created by Giuseppe Mercalli in 1902. This scale studies people’s experiences and building damage to estimate earthquake intensity.

Earthquakes produce three main types of waves: P waves, S waves, and L waves.
L waves cause most of the destruction. In contrast, scientists use P and S waves to study the Earth’s interior.

P waves travel the fastest, so they reach stations first. They are longitudinal waves, where particles move in the same direction as the wave. Like sound waves, P waves move through solids, liquids, and gases.

On the other hand, S waves travel more slowly. They are transverse waves, where particles move sideways. Unlike P waves, S waves move only through solids.